Refrigerating system



Oct; 3, 1944. r-'. 0. URBAN REFRIGERATING SYSTEM Filed July 27, 1943Ihventor: Fred O Liv an,

His Attorney.

Patented Oct. 3, 1944 nnrmenna'rme srs'rEM Fred 0. Urban, Fort Wayne,Ind., assignor to General Electric Company, a corporation of New YorkApplication July 27, 1943, Serial No. 496,321

Claims.

My invention relates to refrigerating systems and particularly to suchsystems which are provided with refrigerant expansion devices of thefixed restrictor or capillary tube type.

A mechanical refrigerating machine commonly comprises a condensing unitand an evaporating -unit. In compression type systems, thecondensingunit comprises a motor driven compressor and an air or liquid cooledcondenser for liquefying the compressed refrigerant. In.order to controlthe flow of refrigerant from the high pressure of the condensing unit tothe low pressure of the evaporating unit, some form of expansion valveor device is necessary. It has been found practicable in many casesto-employ a capillary tube or other device providing a fixed restrictionbetween the condensing unit and the evaporator. Refrigerating machinesequipped with capillary tubes must be designed. specifically for therange of temperatures and pressures within which they are expected to beemployed. The flow of refrigerant through, a F

capillary tube decreases with a decrease in'tfiepressure differenceacross the tube, and even though there is no change in the conditionssurrounding the evaporator, a decrease in condensing pressure mayproduce an objectionable decrease in flow of refrigerant. One important.

tion will become apparent as the following description proceeds, and thefeatures of noveltywhich characterize my invention will be pointedoutwith particularity in the claims annexed to and forming a part ofthis specification.

For a better understanding of my invention, reference may be had to theaccompanying drawing in which Fig. 1 represents diagrammatically arefrigerating system embodying my invention, and Figs. 2 and 3 representother embodiments of my invention.

Briefly, each of the refrigerating systems disclosed in the drawingcomprises a compressor, a condenser and an evaporator connected inseries to provide a normal refrigerant circuit, a capillary tuberestrictor is provided in the circuit between the condenser and theevaporator to con trol the flow of liquid'refrigerant from the highpressure side to the low pressure side of the refrigerant circuit. Arefrigerant storage chamberis connected in restricted communication withthe condensing unit and a controlis pro! vided which causesan-interchange of liquid refrigerant' between the refrigerant circuitand the chamber. The control is actuated in accordance with apredetermined condition of operation of the system, and the effectivecapacity of the system is varied by storing more or less liquid factorwhichis involved in the determination of the range of operation of therefrigerating machine is the quantity of the charge of refrigerantemployed in the system. It has been found, for example, that arefrigerating machine will'prodlice different suction pressures when themachine ischarged with different amounts of refrigerant. The charge ofrefrigerant placed in the system critically determines the practicalrange of operation of the system.

It is an object of my invention to provide a1 refrigerating machineemployingan expansion device of the fixed restrictor type and includingan improved arrangement for increasing the'effecti've range of operationof the machine.

It is another object of my invention to provide a refrigerating machinehaving an expan-' refrigerant in the chamber out of the path of flow ofthe refrigerant in the circuit.

Referring now to the drawing, the refrigeration system shown in Fig. 1comprises an evaporator I 0 arranged in an air duct I I for cooling theair passing therethrough. vaporized refrigerant is withdrawn from theevaporator by operation of a compressor l2, and the hot compressedrefrigerant is cooled and liquefied in a condenser and capillary tubewill operate satisfactorily sion device of the fixed restrictor type andincludtem is operated so that there is no superheat at the evaporatoroutlet the change in refrigerant vided with an expansion device of thefixed restrictor type. i 5

Furthar objects and advantages of my invenwithin a predetermined rangeof operating conditions, the limitations of satisfactory operationdepending upon the quantity ct -refrigerant with .which the circuit ischarged.

I have found that the suction pressure of a refrigerating machine of,the above type'maybe effectively controlled 'by varying the quantity ofrefrigerant in the system. As long as the syscharge results in a changein both the evaporator and the condenser pressures, and by selecting thequantity of refrigerant in the circulating walls of the condenser.

system, the evaporator can be operated at any desired percentage of itsmaximum capacity. The effect of changing the refrigerant charge in asystem such as shown in Fig. 1 is to vary the effective area of thecondenser, the greater' or tank I5 outside the refrigerant circuit andin communication with the circuit through a restricted tube or duct I6connecting the bottom of the chamber with the lowermost portion of thecondenser. Liquid refrigerant flowing from. the condenser I3 fills aliquid line indicated at H as a continuation of the condenser and aportion of this liquid may be cooled by heat exchange with the coldvapor withdrawn from the evaporator through thesuction line indicated atI8. For this purpose portions of the lines I1 and I8 are connected inheat exchange relation at IS. The chamber I5 may be located at anysuitable position where it is normally in an ambient have ing atemperature lower than the condensing temperature of the refrigerant inthe condenser.

In Fig. 1, the chamber I5 i'sarranged in the same The selection oftheabove design structure to provide a long time constant for thechamber and a short timeeconstant for the thermostatic control providesinherent stability. The control bulb or feeler 24 has been shownresponsive to the evaporator inlet temperature only by way of example,it being obvious that the system may be controlled in accordance withother operating conditions if desired. The control as shown in ambientas, the condensing unit. The tube I5 is of sufficiently small diameterto prevent the liqerant circuit through the duct I6 into the tank I5until a state of equilibrium is established. In

order to change the temperature. within the chamber I 5 and therebychange the pressure and the amount of refrigerant stored within thechamber, an electric heater is arranged within a recess 2I in thechamber wall and is energized from a suitable source of electriccurrentbyclosing a switch 22 in accordance with the temperature at the outletof the capillary tube I4. The switch 22 is operated'by a bellows 23actuated in accordance with the pressure within a thermal bulb 24secured'in heat exchange relation with the inlet of the evaporator Illadjacent the capillary tube I4. When the temperature falls the switch 22'is closed and the heater is energized todecrease the amount ofrefrigerant in the chamber I5. If desired, the chamber I5 may beprovided with a covering 25 of thermal insulation to decrease the rateof change of the tank temperature with changes in the temperature of theambient medium. The tank I5is relatively small because a considerablechange in operating conditions may be effected by relatively smallchanges in the amount of refrigerant charge, By selecting theproportions of the'mass and of the insulation of the tank I5, thecapacity of may be of any suitable type and may be made to be sensitiveto small changes and have a low time constant, that is, a rapid responsecharacterist c.

the tube 28 results; however, if the tube 28 is sufficiently restricted,the resulting loss in refrigera'ting efllciency may be made negligible,for

- example, the loss may be made only one tenth of one per cent.

The refrigerating system of Fig. 1 may, for example, be employed in aroom cooler which circulates air over the evaporator Ill and whichprovides for circulation 'of withdrawn air over the condensing unitincluding the compresser I2, condenser I3 and tank I 5. Let us assumethat the withdrawn temperature is 95 F. and that the.

room cooler is maintaining the room air at a dry bulb temperature of F.and a wet bulb temperature at 67 F. These conditions will produce apredetermined average suction pressure and an average head pressuredependent upon the particular refrigerant employed. The chamber might,for example, be somewhat over half 'full of liquid refrigerantand underthe control of the thermostatic switch 22, the heater 20 would befurnishing heat at an average rate to maintain a predeterminedtemperature within the tank I5. If the weather conditions change andlower the outdoor temperature to F., the

head pressure will drop quickly and will reduce the flow through thecapillary tube I4 and result refrigerant flow causes an increase in theevaporator superheat. Momentarily, .at the time off." the change, therewill be a fiow of liquid refrig-1 erant out of the tank but there willalso be evaporation of liquid to fill the displaced volume and thiswillcool the small mass of liquid to a new temperature at whichequilibrium will be reached,

and the flow of liquid refrigerant through the duct I6 'will stop.Further cooling of the tank I5 because of the new low temperatufe of theair circulating around the condensing unit may then reverse the flow andbegin to fill the tank. However, the decrease in eva rator temperatureat the bulb 24 due to the lower pressure will close the switch 22 andsupply heat to the tank I5 and increase the temperature of the tank sothat liquid refrigerant will be forced back into the refrigerantcircuit. The additional liquid refrigerant forced into the circuit willflow back into the condenser and reduce the effective condensingsurface, thereby raising the condensingtemperature, and the increasedamount of liquid refrigerant in the condenser also will cause greatersubcooling of the liquid than before the change. The higher condenserpressure and the greater subcooling results in an increased flow throughthe capillary tube and increases the evaporator capacity to thatrequired to handle the room cooling load.

It was assumed above merely for purposes of example that the change inoperating conditions I was produced by a change in the ambienttemperature of the condensing unit. system also operates to producecapacity changes to meet different conditions due to changes in theevaporator ambient temperature or a com-, bination of changes of bothcondensing and evaporating temperatures. v

The size of the tank I is determined by the volume of the condenser l3and by the proportion of the condenser surface which is to be blockedoff by flooding at the extreme end of the control range. However, exceptfor the additional heat input required to make up for higher loss in alarger tank, there is no objection to making the tank sufficiently largeto contain the entire refrigerant charge of the system. The tank shouldbe located so that it will drain completely by gravity during theshutdown period; this minimizes the accumulation of oil in the tank.-

The modification of my invention illustrated in Fig. 2 is similar tothat of Fig. 1 and corre-' sponding parts have been designated by thesame numerals. The system of Fig. 2 differs from that of Fig. 1 in thearrangement for controlling the interchange of liquid refrigerantbetween the refrigerant circuit and the tank l5. In Fig. 2, athermosiphon pump comprising a. liquid leg and a liquid-vapor leg 3! isconnected be-,

tween the lowermost portion of the liquid line l1 and the vapor spacebetween the upper portion of the tank l5. When it is desired to supplyliquid refrigerant to the tank IS, an electric heater 32 is energizedand heats liquid in the leg 31 to vaporize a portion of the liquid andchange the average density of the refrigerant. in that portion and alsoto produce a vapor lift A resulting in a flow of liquid refrigerant fromthe liquid line I1 to the chamber I5. The return of liquid refrigerantfrom the chamber l5 to the line I! is effected through a restricted duct33 connectingthe bottom of the tank with the liquid line H. The duct 33tends-to drain the tank l5 at a substantially constant rate and thethermosiphon pump is designed to provide a maxi-- mum rate of flow of,say, twice the rate of flow through the duct/33. It is thus apparentthat by control of the thermosiphon pump the average amount of liquidrefrigerant in the chamber l5 may beheld at any predetermined desiredaverage level. The electric heater 32 has been shown connected toasuitable source .of alternating current through a transformer 34 and theswitch 22. In order to prevent any appreciable change in the operationof the thermosiphon pump because of the saturation pressure-temperaturecharacteristics of the refrigerant, a. pressure equalizing tube 35 isconnected between the vapor space of the chamber l5 and the highpressure vapor space of the condensing unit, that is the high pressurespace between the compressor discharge "port and the liquid in thecondenser.

The operation of the system shown in Fig. 2 is essentially the same asis shown in Fig. 1 except that the changes in level of the liquidrefrigerant in the tank I5 are effected solely by However, the

energization of the heater 32.

the operation of the thermosiphon pump and no substantial transientchanges are produced due to changes in the saturation pressuresandtemperatures.

In Fig. 3, I have illustrated another modification of my invention whichis similar to that shown in Fig. 2 and corresponding parts have againbeen designated by the same numerals. The difference between the systemsof Figs. 2 and 3 lies in the arrangement for controlling the In Fig. 3the heater is controlled in accordance with the amount of superheat inthe vaporized refrigerant returned to the compressor instead of inaccordance with the inlet evaporator temperature.

Theheater 32 is energized by the operation of a thermal bulb '4!responsive to the temperature the evaporator.

" to energize the heater 32.

tur'es,

frigerating systems inwhich the control is'deat the outlet of theevaporator. The bellows 38 tends to open the switch 31 upon an increasein temperature at the inlet of the evaporator, and the bellows 39 tendsto close the switch 31 upon an increase in the temperature at the outletof The difference between these temperatures is dependent upon thesuperheating of the refrigerant vapor withdrawn from the evaporator andthe systein is therefore controlled in accordance with suction vaporsuperh eating. It is obvious that other forms of superheat sensitivecontrols knowntothe art may be employed The arrangement of Fig. 3 is thepreferred control for'dry expansion systems but may be employed equallywell on flooded systems; the control arrangements of Figs. 1 and 2 areprimarily for systems employing normally flooded evaporators.

In the foregoing description it has been assumed by way of example thatthe-changes in operating conditions are produced by changes in theambient temperature of the condensing unit.

It is obvious, however, that the changes mayv be produced by othercauses such as changes [in evaporator ambient temperature or in bothevaporator and condensing unit ambient tempera.-

Furthermore, it is recognized that rependent merely upon the evaporatorpressure may be required to operate under certain unfavorable conditionswhich produce unsatisfactory operation because of the characteristics ofthe control. It is obvious,' therefore, that the use of a particulartype of control for a refrig- It will be noted in Figs. 2 and 3 that noheat interchanger has been employed between the liquid line and thesuction line. Such heat interchangers are frequently employed to betterthe economy of the system but are not essential to the operation of thesystem.

It is readily apparent from the foregoing that I have provided a.simple'and effective arrangement for varying the efiective capacity ofa. refrigerating machine employing an expansion device of the fixedrestrictor type and that my in- Letters Patent of the United States is:

1. A refrigerating system comprising a compressor and a condenser and anevaporator con-.

nected in series to provide a normal refrigerant circuit, a fixedrestrictor in said circuit for controlling the flow of refrigerant fromsaid conerant storage chamber arranged outsidethe normal series path ofrefrigerant in saidcjrcuitand having restricted communication affordingpas-" sage of liquid refrigerant between said chamber and saidcondenser, and means dependent upon a condition of operation ofsaidsystem for varying the ratio of the amount of refrigerant in saidchamber to the amount in said circuit to vary the capacity of saidsystem.

2. A refrigerating system comprising av compressor and a condenser andan evaporator connected in series toprovi'de a normal refrigerantcircuit, a fixed restrictor in said circuit for controlling the flow ofrefrigerant from said condenser tosaid evaporator, a closed liquid refri5. A refrigerating system comprising a compress'or and a condenser andan evaporator connected in series to provide a normal refrigerantcircuit, a fixed restrictor in said circuit for con-' trolling the flowof refrigerant from said condenser to said evaporator, a closed liquidrefrigerant storage chamber arranged outside the normal series path ofrefrigerant in said circuit and having restricted communicationaffording passage of liquid refrigerant between said chamber and saidcircuit, means including a thermosyphon pump for conveying liquidrefrigerant from said circuit'to said chamber, and means dependent upona condition of operation of said system for operating said pump todetermine the amount of refrigerant stored in said chamber whereby thecapacity of said system is varied in accordance with said condition ofoperation.

6. A refrigerating system comprising""a condensing unit and anevaporating unit and a dried restrictor for controllin the flow ofrefrigerant from said condensing'unit to said evaporating unit, meansincluding a closed thermally indenser to said evaporator, a closedliquid refrigerant storage chamber arranged outside the normal seriespath of refrigerant in said circuit and having restricted communicationaffording passage of liquid refrigerant between said chamber and saidcondenser, and means dependent upon the temperature of the refrigerantadmitted to said evaporator for controlling the interchange of liquidrefrigerant between said chamber and said circuit to vary the capacity-of said system.

3. A refrigerating system comprising a compressor and a condenser and anevaporator connected in series'to provide a normal refrigerant circuit,a fixed restrictor in said circuit for controlling the flow ofrefrigerant from said condenser to said evaporator, a closed liquidrefrigerant storage chamber arranged outside the normal series path ofrefrigerant in said circuit and having restricted communicationaffording passulated chamber for storin a quantity of liquid refrigerantand for restricting the circulation of said quantity of liquidrefrigerant through said system, and means dependent upon a condition ofoperation of said system for effecting an interchange of liquid betweensaid system and said chamber for varying the ratio of the amount ofrefrigerant in said chamber to the'amount in the remainder ofsaid-system whereby the capacity of said system is varied in accordancewith said condition. I v

' .7. A refrigerating system comprising a condensing unit and anevaporating unit and a fixed restrictor for controlling the flow ofrefrigerant from said condensing unit to said evaporating unit, meansincluding a closed thermally in-' .sulated chamber for storing aquantity of liquid refrigerant and for preventing the circulation ofsaid quantity of liquidrefrigerant through said sage of liquidrefrigerant between said chamber and said condenser, and means dependentupon a condition of operation of said system for sunplying heat to saidchamber to determine the amount of refrigerant stored in saidchamber.whereby the capacity of said system is varied in accordance with saidcondition of operation.

4.- A refrigerating system comprising a comp essor and a condenser andan evaporator connected in series to provide a normal refrigerantcircuit, afixed restrictor in said circuit for controlling the flow ofrefrigerant from said con denser to said evaporator, a closed liquidrefrigerant storage chamber arranged outside the normal series path ofrefrigerant in said circuit and having restricted communicationaffording passage of liquid refrigerant between said chamber and saidcondenser, and means dependent upon the difference in temperaturebetweenthe inlet of said evaporator and the'outlet thereof andcontrolling the relative amounts of refrigerant in said chamber and insaid circuit for varying the capacity of said system.

system, means including a thermosyphon pump and a restricted return ductfor effecting an interchange of liquid refrigerant between said systemand said chamber, and means dependent upon a condition of operation ofsaid system for actuating said pump to determine the relative amountsofrefrigerant in said chamber and in the remainder of said system.

8. A refrigerating system comprising a condensing unit and anevaporating unit and a fixed restrictor for controlling the flow ofrefrigerant from said condensing unit to said evaporating unit, meansincluding a closed chamber arranged in an ambient having a temperaturelower than the condensing temperature of refrigerant in said system forstoring a quantity of liquid refrigerant and for restricting thecirculation of said quantity of liquid refrigerant through said system,and.

means dependent upon a condition of operation of said system foreffecting an interchange. of

- liquid between said system and said chamber for varying the ratio ofthe amount of refrigerant in said chamber to the amountin the remainderof said system whereby the capacity of said system is varied inaccordance with said condition.

9. A refrigerating system comprising a compressor and a condenser and anevaporator connected in series'to provide a normal refrigerant circuit,said circuit including a fixed restrictor for controlling the flow ofrefrigerant from saidrcondenser to said evaporator, a closed liquidrefrigerant storage chamber arranged outside the normal series path ofrefrigerant in said circuit and and said circuit whereby liquidrefrigerant may in the upper portion of said chamber for conveyin;liquid refrigerant from said circuit to said chamber, means dependentupon a condition vof restrictor for controlling the flow of liquidrefrigerant irom said condensing unit to said evapoperation of saidsystem for operating'said pump to determine the amount of refrigerantstored in said chamber whereby' the capacity of said 7 system is variedin accordance with said condition of operation, and a restricted ductconnect-' 10.- A refrigerating system comprisin a con densing'unitand-an evaporating unit and a fixed orating unit, means providing aclosed chamber having restricted communication with said condensing unitfor storing a quantity of liquid refrigerant and for restricting thecirculation .of said quantity of liquid refrigerant through said system.means dependent upon a condition 01 operation of said system for heatingsaid chamber to eflect an interchange of liqui between aid condensingunit and said chamber for varying the capacity of said system inaccordance with said condition, and a restricted duct connecting said,chamber above the level of liquid therein with a relatively low pressureportion oi fsaid condensing unit for removing noncondensabie gas fromsaid chamber.

I FRED 0. URBAN.

